With advances in drilling technology it has become increasingly common to drill oil and/or gas wells that have sections that are deviated from a vertical orientation. In some wells one or more sections may be at least partially horizontal. A well with such a horizontal section may also be referred to as non-vertical well, a lateral well, a deviated well or a horizontal well. As a method to increase production from these horizontal wells the wellbores are first cased. The casing may then be perforated or otherwise opened in intervals at specific locations.
Various approaches are used for creating an opening or perforation in the casing. Such approaches include, but are not limited to: explosive perforating, use of screens and sliding sleeves, burst discs, and abrasive jetting each of which can provide fluid communication between the inside and outside of the casing.
Next a portion or all of the horizontal wells can be subjected to a fracturing operation. The fracturing operation generates cracks within a geologic formation surrounding the horizontal well. The cracks provide a fluid pathway for facilitating fluid communication between the wellbore and an oil and/or gas containing reservoir within the geologic formation. Different fracturing methods are used to generate the cracks including, but not limited to pumping a high-pressure fracturing mixture of fluid and proppant into each stage of well and the local geological formation individually. Fracturing surface-pressures and flow rates are monitored to determine the breakdown pressures and effectiveness of the fracturing operation. However, things can go wrong while pumping the fracturing mixture. For example, sand within the fracturing mixture can plug off flow through one or more cracks; pumps can malfunction; and characterization of the reservoir resistance can be inaccurate. These and other known issues can result in a less-than-ideal fracturing operation.
It also common that different portions of the same geologic formation will respond differently to the fracturing operation. This can result in different production rates between the stages of the horizontal well. The cracks tend to follow the path of least resistance in the geologic formation, which results in complex flow paths for the fluids to flow from the reservoir to the wellbore. The width of the fracture, the tortuosity of the fluid path and the amount of proppant in the fracture can all affect the production rate of fluids through a given crack.
Furthermore, one or more stages of the well may end up producing water from the geologic formation. For example, one stage may intersect with a water layer and produce more water than other stages of the horizontal well. Water has lifting and separating costs that impact the economics of the well's production. There are known methods that attempt to improve the well's economics by reducing the quantity of produced water using plugging gel fluids or mechanical shut-off devices. These methods require, however, that the well operator knows which stages of the well are producing the problematic water.
It has been estimated that only 25% of the fractured stages in a horizontal well provide significant oil and/or gas production. Very few direct measurements of each individual stage have been done because there are limited efficient manners to measure the characteristics of the fractured sections portions of the geologic formation or the nature of the fluids that are produced therefrom. Most measurements, such as a draw-down test, are performed on a well as a whole collective-unit by measuring a pressure response from the well based on rate changes provided at surface.